Michigan State University Extension
Ornamental Plants plus Version 3.0 - 00000942
11/12/99
MALUS DISEASE PROBLEMS
Scab is caused by the fungus Venturia inequalis.
Infection takes place early in the season and dark olive
green spots (Vis. 1) appear on the leaves. In late summer
the infected leaves fall off when they turn yellow with
black, spots. Infected fruits have black, slightly raised
spots. Use resistant varieties.
Fire blight susceptible trees have blighted branch tips.
The disease is caused by the bacterium Erwinia amylovora.
Leaves on infected branch tips turn brown or black, droop,
and hang on the branches (Vis. 3). The leaves look scorched
as by a fire. The trunk and main branches become infected
when the bacteria are washed down the branches. Cankers
form and are separated from adjacent healthy bark by a
crack. The infected bark may be shredded. There is no
satisfactory chemical control for fire blight. Use
resistant cultivars when available.
Powdery mildew coats leaves with white powder.
Rust causes brown to rusty-orange spots (Vis. 2) on the
leaves. Red cedars are the alternate host. Badly spotted
leaves fall prematurely.
Crab Apples are subject to several canker diseases. Avoid
unnecessary wounding, keep trees healthy, and prune out
infected branches when seen.
Related information.
Pesticide Recommendations
Cedar-apple Rust
Powdery Mildew
Cankers
Scab
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This file was generated from data base ZZ on 01/19/00.
Data base ZZ was last revised on 11/12/99.
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